1. Field of the Invention
The present invention relates to a mass spectrometer and a mass spectrometry method and, for example, a mass spectrometer and a mass spectrometry method which analyze a sample in at least one of solid and liquid state easy to pyrolytically decompose by ionizing it using an ion attachment method to suppress decomposition.
2. Description of the Related Art
An ion attachment mass spectrometer (IAMS) is an apparatus which attaches ions to target measurement molecules and measures their mass.
Ion attachment mass spectrometers are reported in non-patent references 1, 2, 3, 4, and 5. Related techniques are disclosed in patent references 1, 2, 3, 4, 5, and 6.
FIGS. 9 and 10 show examples of mass spectrometers for analyzing the mass of a solid and/or liquid sample. Both mass spectrometers use an ion attachment method for ionization.
An ionization chamber 100 and a sample vaporization chamber 101 are arranged in a first cell 130. A mass analyzer 108 is arranged in a second cell 140. Vacuum pumps 109 evacuate the first cell 130 and the second cell 140. Hence, all the ionization chamber 100, sample vaporization chamber 101, and mass analyzer 108 are maintained in a low pressure atmosphere having a pressure lower than the atmospheric pressure. An emitter 107 made of a metal oxide and placed in the ionization chamber 100 generates positively charged metal ions such as Li+ when heated.
A sample 105 is held by a sample holder 104 arranged in the sample vaporization chamber 101, and heated by an indirect heater 103. The indirect heater 103 and the sample holder 104 are provided at the distal end of a sample insertion probe 102. The solid and/or liquid sample 105 heated in the sample vaporization chamber 101 vaporizes and turns into neutral gas phase molecules (gas) 106. The neutral gas phase molecules 106 move and enter the ionization chamber 100 by diffusion, gas flow and buoyancy, and the like.
Then, the neutral gas phase molecules 106 are ionized in the ionization chamber 100 to generate ions. The ion attachment method attach metal ions to the portions of the neutral gas phase molecules, that have dielectric polarization. The molecules with the metal ions attached form ions that are positively charged overall. The molecules do not decompose because the energy given to them upon metal ion attachment is very small.
The generated ions are transported from the ionization chamber 100 to the mass analyzer 108 upon receiving a force from an electric field, and analyzed by the mass analyzer 108.
The ion attachment method capable of ionizing original molecules without decomposing them is advantageous because it allows highly accurate, quick, and simple measurement. More specifically, a mass spectrum measured by the ion attachment method has no decomposition peak but only the original molecular peak. In short, a sample containing n kinds of components exhibits n peaks, and the components can be qualitatively and quantitatively measured based on their mass numbers. It is therefore possible to directly measure even a mixed sample containing a plurality of components without component separation.
In techniques other than the ion attachment method, various kinds of decomposition peaks appear in a mass spectrum. It is therefore necessary to separate components using a gas chromatograph (GC) or a liquid chromatograph (LC) before mass analysis. To normally separate the components of many samples by GC/LC, complex and cumbersome preprocessing is required for each sample. Normally, component separation takes several ten minutes, and preprocessing takes several to several ten hours. The ion attachment method requires neither preprocessing nor component separation and can end measurement in only several minutes.
However, in some samples, molecules may decompose (pyrolytically decompose) simultaneously with vaporization. Such a sample cannot generate ions in the original molecular state because of decomposition at the time of vaporization even if decomposition at the time of ionization is suppressed using the ion attachment method.
As a technique of vaporizing a sample easy to pyrolytically decompose without pyrolysis, a rapid heating method is known. This method quickly heats and vaporizes a sample before the start of pyrolysis. However, in the apparatus shown in FIG. 9 called a direct inlet probe (DIP), the indirect heater 103 heats not only the sample 105 but also the sample holder 104 and the sample insertion probe 102 having large heat capacities. Hence, rapid heating is difficult. This method generally takes several minutes to reach the vaporization temperature.
An improved apparatus shown in FIG. 10 called a direct exposure probe (DEP) can perform rapid heating because a direct heater 110 heats only the sample 105. The time to reach the vaporization temperature shortens to several sec. However, many samples still pyrolytically decompose even in this method. Additionally, since the sample vaporization chamber 101 is away from the ionization chamber 100, a sample that has escaped pyrolysis upon vaporization may pyrolytically decompose during movement to the ionization chamber 100.
An apparatus shown in FIG. 11 called a particle beam apparatus is used as an interface to a liquid chromatograph/mass spectrometer (LC/MS) for continuously measuring a solution sample made by dissolving and mixing sample components in a medium (solvent). In the particle beam apparatus, a solution sample 125 is turned into fine particles by a sprayer 124, vaporized (to neutral gas phase molecules) in a heated sample vaporization chamber 123, and introduced into the ionization chamber 100. In the sample vaporization chamber 123, the solvent that impedes measurement is removed and discharged to concentrate the sample. A separator 120 ejects the vaporized gas to the discharge area of an exhaust pipe 121, passes only heavy molecules (sample components), and discharges light molecules (solvent). A heater 122 heats the sample vaporization chamber 123.
However, a component having a high vaporization temperature may enter the ionization chamber 100 in a fine particle state without being vaporized sufficiently. Alternatively, a component easy to coalesce (independent molecules gather to form an aggregate) may form fine particles after vaporization in the sample vaporization chamber 123 and enter the ionization chamber 100.
As the ionization method, electron ionization (EI) is used as a common ionization technique for neutral gas molecules.
Electron spray ionization (ESI) that is the most popular ionization method of LC/MS directly ionizes a solution sample (without vaporizing). This reduces the influence of pyrolysis. Note that both the electron ionization (EI) and the electron spray ionization (ESI) cannot ionize a sample while suppressing decomposition.
GC/LC measurement using these methods not only takes time and labor but also requires an expensive internal standard sample for quantitative measurement. LC measurement requires an internal standard sample because preprocessing and component separation are done in many process steps, and comparison of absolute values is impossible. To the contrary, the ion attachment method that requires neither preprocessing nor component separation can perform quantitative measurement without using an internal standard sample.
It is demanded to quickly, accurately, simply, and inexpensively measure the mass of a solid or liquid sample without decomposing its molecules regardless of components and the presence/absence of a solvent.
[Patent Reference 1] Japanese Patent Laid-Open No. 6-11485
[Patent Reference 2] Japanese Patent Laid-Open No. 2001-174437
[Patent Reference 3] Japanese Patent Laid-Open No. 2001-351567
[Patent Reference 4] Japanese Patent Laid-Open No. 2001-351568
[Patent Reference 5] Japanese Patent Laid-Open No. 2002-124208
[Patent Reference 6] Japanese Patent Laid-Open No. 2002-170518
[Non-Patent Reference 1] Hodges (Analytical Chemistry vol. 48, No. 6, p. 825 (1976))
[Non-Patent Reference 2] Bombick (Analytical Chemistry vol. 56, No. 3, p. 396 (1984))
[Non-Patent Reference 3] Fujii (Analytical Chemistry vol. 61, No. 9, p. 1026 (1989))
[Non-Patent Reference 4] Chemical Physics Letters vol. 191, No. 1.2, p. 162 (1992)
[Non-Patent Reference 5] Rapid Communication in Mass Spectrometry vol. 14, p. 1066 (2000)